Aspects of the present invention relate generally to the field of video processing, and more specifically to a predictive video coding system.
Video display systems impart a sense of moving video when multiple images are displayed at a rate of 10 frames/second (fps) or more. Video coding systems attempt to convey motion by coding a video sequence and transmitting it over a bandwidth-limited channel. Channel bandwidth can vary in many systems, however, without warning. Video coding systems dynamically alter parameters of the video sequence (quantization parameter, coding modes, frame size and frame rate) to fit the coded video data to the bandwidth provided by the channel. Video coding protocols are lossy processes and, therefore, some coding parameters can lower the perceptual quality of the recovered video.
In some cases, however, bandwidth restrictions become so severe that an encoder must drop the frame rate to a level that the recovered video ceases to be perceived as “moving” video. At 1-3 fps, for example, recovered video likely is perceived as a series of still images (analogous to a slide show effect) rather than moving video. Consumers perceive the quality of coded sequences to be particularly bad when visually unappealing images—blurred images, under-exposed images, etc.—are displayed at a terminal for a prolonged period of time. The inventors, therefore, perceive a need in the art for a coding control scheme that, during severe bandwidth restrictions, selects high quality images for coding.